Fatigue-testing machine



.im 11, 1944. R EKSERGIAN Re. 22,416

FATIGUE-TESTING MACHINE Original Filed Aug. 3, 1940 3 Sheets-Sheet 1 Mr -w- 53 SYM/MV ATTORNEY Jan. ll, 1944. R. EKSERGIAN FATIGUE-TESTING MACHINE Original Filed Aug. 3. 194D 3 Sheets-Sheet 2 INVENTOR Eupen ,E'sergzan Jin u, 1944- R. EKsr-:RGIAN FATIGUE-TESTING MACHINE Original Filed Aug. 3. 1940 3 Sheets-Sheet 3 2 W3 W-RES. M W5 W6 FREQUENCY W Gmo Q M W 6 w E m u R TIME' A TTORNE Y Ressued Jan. 11,1944

FATlGUE-TESTING MAHINE ltupen Ekserxian, Lansdowne, Pa.,

Edward G. Budd Manufacturing assigner to Campi-uv.

Philadelphia Pa., a corporation of Pennsylvania Original No.

No. 350,854, August 3, 1940. reissue September 18, 1943, Serial No.

13 Claims.

The present invention relates to the testing of materials. More specincally it relates to mechanism for testing articles as to their capability of withstanding repeated stresses, that is, their capability of resisting fatigue. especially when subjected to periodic or vlbratory stresses.

The invention contemplates a testing machine based on the principle of a vibration beam suitably damped thus controlling the amplitude of vibration and permitting an initial loading to be applied through the beam system to'the specimeh. A motor mounted to the beam with eccentric counter-weights is used as an external alternating impressed force on the system. It is lil well-known that a simple vibration system hasl its own natural period of vibration depending on the proportions of the mass and elasticity oi the system. The vibration system Y in this testing machine consists essentially of the vibration beam hinged to one end and free to rotate about this hinged point as the inertia element. The beam is constrained in turn by helical springs, one below the beam and one above the beam, the latter of which is connected to the specimen. Neglecting the small elasticity of the specimen, the elastic system consists essentially on the top and bottom springs. The testing vibration beam can be turned to any natural pre-concelved operation by the proper selection of the inertia properties of the beam about its hinged points and the elastic properties of the spring. 0n the basis of a forced vibration, it is weliknown that in approaching resonance, that is in approaching a speed corresponding to the natural frequency of the system, large amplitudes will occunjunless suitable damping is provided for. In this testing system the amplitude is controlled by a damping device when the speed of the motor vibrator approaches the natural frequency of the beam system.

An important feature of this machine is that it makes possible the testing of alternating loaditms superimposed on an initialor pre-load. I'his is accomplished by a jack placed beneath the bottom spring and jacking up the entire system so that the upper spring applies a definitepre-load on the specimen. On starting the motor vibrator, the machine is brought up to a speed approaching resonance and the amplitude over and below the mean loading is controlled .by means of the damping device. This control can also be made by a change in speed of the motor with a fixed damping course or by both methods. Thus a sensitive control of amplitude for vibraon a pre-load is attained.

o lilla-.e

2,317,097, dated April 20, 1943, Serial Application for The pre-loading can be given any value whatsoever by changing the adjustment of the lack.

A speciilc example of such machine is described in the following speciiication and illustrated in the drawings accompanying the same, wherein:

Fig. 1 is a diagrammatic side elevation of the fatigue testing machine:

Fig. 2 is a plan view thereof, partly in horizontal section on the planes indicated by the broken line 2-2 of Fig. l;

`flig. 3 is a fragmentary vertical section on the planes indicated by the broken line 3-3 of Fig. l, and on an enlarged scale;

Fig. 4 is a fragmentary sectional detail, also on an enlarged scale, on the plane indicated by the line l-l of Fig. 1, showing the excentrically mounted rotary inertia member for producing the vibrations;

Fig. 5 is a fragmentary detail view of the adjustable inertia member on a still larger scale, showing the casing surrounding the same:

Fig. 6 is a corresponding horizontal section therethrough on the plane indicated by the line 8-8 of Fig. 5;

Fig. 'I is a fragmentary detail on an enlarged scale, showing the scale, and the pointer carried by the beam to cooperate therewith, to indicate the amplitude of the vibrations, this gure being partly in section on the plane indicated by the line 'l-l of Fig. 2; and

Figs. 8 and 9 are diagrams illustrating the principle of the function of the machine.

In all the ilgures similar elements are indicated by the same reference characters.

Referring first to Fig. 1, the device comprises a base I mounted on any suitable, door or support 2 by yieldable or resilient means, such as the springs 3 which act as shock absorbers, leaving the base I and the parts mounted thereon free to vibrate, while at the same time preventing any disagreeable vibration from reaching the floor 2.

A vertical column I is mounted on the base I near one end o1' the latter. This column has lugs or bosses i therein which support a shaft t, nuts 1 being provided to retain the shaft in position. The shaft I serves as a pivot for the substantially horizontal ann or beam 8 which is mounted so as to be free to turn about said shaft except as restrained by other parts of the mechanism.'

At or near the other end of the base I a substantially vertical guide or column 9 is mounted. 0n a bracket Il of the column I is adjustably arranged a scale il, auch as by the screws Il passing through slots El. The scale II may be placed at the proper height to cooperate with a pointer I3 carried at il by the free end oi the arm t, so that the position of the arm 8 may thus be read on the scale.

A compression spring I4 bears in a cup i5 on the underside of the arm l and is supported in an opposed cup I6 at its lower end. A lifting device such as a screw-jack having a base member I1, diiierential screws lli and Il of the customary type and a plate 2l, is inserted between the base plate I and the lower end ofthe spring Il.

The base I also carries damping means. 'I'hese means comprise a cylinder 2| iilled with a tluid, and within which operates a piston 22 at one end of a rod 23. The cylinder 2l is pivotally mounted on a base 2l by means of the pin 2B, and the piston rod 23 is pivotaliy attached to the tting 26 on the beam 0, by means oi' the pivot 21.

The means for producing the vibratory motion of the arm l comprises a motor 28 mounted on a base 29, the latter being secured to the arm 8 by bolts 88. The shaft In of said motor is connected by a suitable coupling Il to the shaft 32 of a speed-reducing gearing also mounted on the arm 8 by means of a suitable base 3l. This gear comprises a worm B6 on shaft 32 and a worm wheel 61 on a shaft 1I, the latter being supported by bearings 1li. A hollow member 38 is fastened to shaft 1I. A projecting enclosure 31 may be provided for the casing 36. The casing contains a weight or inertia element 12, which is adiustably supported by the threaded shaft 1B, the latter being held by collars 18 and being provided with square heads 11. said weight 12 projects through slot 18 in cover plate Bil and carries a hand 18 playing over a scale ll, Il and 8l are set screws and lock nuts for holding the member rigidly in the casing 36.

A further resilient means, such as the spring 38, is mounted upon a suitable base l carried by the beam I and bears against a cooperating cup lt placed on top of the spring, said cup III having an extension 4I which may be secured. such as by a pin connection 4I' to the test specimen I2 or may in' certain cases merely abutV against the specimen. The specimen is rigidly fastened to a supporting plate l' at the upper end oi' column l.

Links 4i may be provided at two opposite sides of the spring l., and these links may be pivotaily secured to the beam l such as by pin 44 held in place by the cotter pins Il, and to the cup III by pin 41 being connected to said cup lll and passing through slots Il. This construction prevents disengagement ci the parts when the test piece is removed.

In order to secure the required strength, the column l is built up with webs or anges Il, I9, and l and a channel member Il.

The greater part of the beam is shown to be an I-beam structure. At the pivotal end an opening 52 is formed in the web of the I-beam to receive the sleeve il. Plates ll and B5 are welded or otherwise secured both to the sleeve and to the flanges of the I-beam l to provide a rigid connection between the sleeve and the said I-beam. Suitable bearing bushings Si, or if preferred roller bearings, may be provided to pivotally support the sleeve 5l on the shaft l, which may have shoulders as shown at I1, to retain the bearing members Ii in proper posinon. 58 are spacing washers.

At the other end. a bracket il is secured at A pin 18 on:

62 to the upper side of beam 8. Above the upwardly projecting end 63 of the bracket 6|, is located a contact device 64, which will be actuated when the end 63 strikes it and will control a safety device 65 of any suitable kind to shut 01T current from the motor in case the amplitude of motion of the free end of the beam 8 for any reason should become excessive enough to cause 63 to strike B4.

Shaft 1I is connected to a smaller shaft 35, and the'latter controls by means ot a coupling 85, a shaft 86 and gearing B1, a revolution counter 88 mounted on a bracket 89 carried by the beam The operation of the device is as follows:

A specimen, such as diagrammatically illustrated at l2, is 4secured to portion 4' of the column l and at another portion to the plunger 4|. Then the jack I1-20 is adjusted t0 compress the springs Il and 38 until the end of the specimen is under the desired mean load.

The violence of the vibration may partly be controlled by varying the position of the weight 12 by means of the screw 15. The frequency is,

of course, dependent upon the speed of the motor 2B, and the gear ratio of the reduction gearing, and may thus be controlled by varying the speed of rotation of the motor, or by changing the gear ratio, or both. The scale Il is preferably so adjusted that the pointer Il plays over its mid-position and the amplitude of the vibration will thus be indicated thereon.

The dashpot device 2|, 22, and 23 will restrain the vibration to a degree dependent upon the adjustment of said dashpot, which thus affords an auxiliary means for controlling the amplitude of the vibration. The register 8B will give a count of the number of vibrations to which the test piece has ben subjected, proper multiplication being made in accordance with the ratio of the gearing 81. If the vibration should become excessive. due, for instance, to resonance conditions or rupture of the article under test, the opstanding end of the bracket 6I will strike the cooperating member Bl of the electric controller and will thus either shut ci! the device entirely or reduce the power supply to the motor to such extent that the vibration will again be decreased to a suitable safe amount.

The principle of the invention shall now be explained by means of the diagrams of Figures 8 and 9. The vibratable system comprising the beam 8, the springs I4 and 18 and the other members supported by the beam-yet disregarding at first the damper 2 I 22-has specific vibration properties. The relation between the frequency W and the amplitude X of this system is diagrammatically shown by the curve A in Figure 8. In approaching the resonance frequency W-RES of the system, the amplitude X would theoretically become infinite. By imparting vibrations oi' a certain frequency, for instance the frequency WI and W6, any desired amplitude X on the curve A may be achieved as for instance indicated by the points XI and X8. This regulation of the frequency gives, however. very little choice regarding the selection of am.- plitude and frequency to which the specimen can be subjected but to one amplitude belong only two specinc frequencies.

It is, on the other hand, obvious that, for imitating conditions as they will arise in the actual use of a structure, it is desirable to coordinate wlthin certain limits any frequency of vibration and any amplitude. 'I'his goal is achieved by the adiustable damping ci the swinging system by means of the damper 2|, 2,2. I! the system is damped, the curves of irequency and amplitude may take, dependent on the degree of damping, the form oi' the curves B or C of Figure 8. It is now possible to coordinate to the amplitude or the previously-mentioned points Xi, X6 any frequency between the frequencies Wi and W3, such as the frequencies W2, W3, Wl or Wi to which the points X2, X3, X4 and X5 on the curves B and C, respectively, belong. It will be understood that the number of curves similar to the curves B and C below the curve A is infinite and that, therefore, within the natural limits of the system any desired' frequency can be combined with any desired amplitude.

The amplitude is, as will be understood, a measure for the variations of load to which the specimenis subjected. By jacking up the spring I4 together with the beam B and the spring 38 by means oi' the jacks I1 to Ill, the specimen willbe subjected to a mean load U which is indicated in Figure 9 by a horizontal straight load line. The variations of the load which are due to the vibrations ofthe system are superimposed on this mean load and are indicated in the load-time diagram of Figure 9 by the curve D. The amounts of these variations in the load to which the specimen is subjected are designated in Figure 9 by X' and they are, as indicated before, a function of the amplitude X of the swinging system.

The invention is not restricted to the specific form of the machine shown in the drawings but it is obvious to those skilled in the art that all kinds of modifications and variations may be designed. It is among other things not necessary to use a beam which is journaled to the base, but the swinging mass may be guided by other means or may even be freely suspended between Vthe two spring systems. It is also not necessary to arrange the beam horizontal, but any other arrangement, such as a vertical arrangement, would serve the purpose, Any means for imparting the vibrations to the swinging arm or mass may be used instead of the specific means shown in the embodiment, the same being true for the damping device and for the jack. Regarding the jack, it may be mentioned that its arrangement between the base and the' Spring Il is no necessity but that it may be arranged at any place in the chain formed by the springs and the beam between the base and one point of the specimen.4 Finally, it may be mentioned that the new machine can easily be modied so as to subject the specimen to tensional stresses instead of to the compres- I sion stresses in accordance with the shown embodiment. All those modincations and variations and others which are not speciiically mentioned are intended to he covered by the spirit and the language of the following claims.

What is claimed is:

1. In a device for testing materials a substantially rigid base, a stationary securing means for attachment to a point oi a specimen to be tested, said means being rigidly supported by said base, a substantially rigid member pivotally supported by said base, means for imparting oscillatory motion to said member about its pivot, and a means in the nature oi a spring being carried by sad member and being adapted for attachment to another point oi the specimen.

2. In a device for testing materials, a substandaily rigid base, a stationary securing means for attachment to a point oi a specimen, said means mi 118ml? Supported by said base, a substan u tially rigid beam pivotally supported at one point oi' its length by said base, means for imparting oscillatory motion to said beam about its pivot, means for controlling the amplitude of said motion, a means in the nature of a spring being inserted between said base and said beam. and a second means in the nature ot a spring being connected with a point oi said beam remote from its pivot and being adapted for attachment to another point oi the specimen.

3. In a device tor testing materials, a base, a stationary securing means, for attachment to a point of a specimen, said means being rigidly supported by said base, a beam pivotally supported by said base, means for imparting oscillatory motion to said beam about its pivot, a. supporting means in the nature of a spring for the beam, and a means likewise in the nature of a spring being carried by said beam and being adapted for attachment to another point of the specimen under test.

4. In a device for testing materials, a base, stationary securing means for attachment to a point of a specimen, said means being rigidly supported by said base, a beam pivotally supported at one end by said base, means for imparting oscillatory motion to said beam about its pivot, meansv for controlling the amplitude of said motion, resilient means supporting said beam, means for adjustably pre-loading said resilient means, and a second securing means carried by said beam adapted for attachment to another point of the specimen.

5. In a fatigue testing machine, a base structure, a vibratable member, a nrst means in the nature of a. spring inserted between said base and said vibratable member, a second means in the nature of a spring adapted to be inserted between said member and one point of a specimen, means for rigidly securing the specimen to said base, means for imparting a vibratory impulse to said member.

6. In a device for testing materials, a base, means -on said base for holding a specimen in one region or point thereof, a vlbratable member, means for imparting oscillatory motion to said member, supporting Vmeans in the nature of a. spring for the member, another means in the nature oi a spring being carried by said member and being adapted for engagement to another region or point of the specimen under test at a substantial distance from the first-named point or region.

7. In a testing machine acordlng to claim 6, means for imparting an initlalor pre-load on said means in the nature of springs and thereby on the specimen.

8. In a testing machine according to claim 6 means for damping the amplitude oi said vibratable member, said damping means being adjustable so as to vary the damping effect.

9. In a. testing machine according to claim 6 means Vfor damping the amplitude of said member; said means for imparting a vibratory impulse being adjustable so as to vary the frequency of the impulse; said damping means being adinstable so as to vary the damping effect; coordination oi the adjustments oi' the damping means and of the vibration means determining together with the natural frequency of the system the frequency and amplitude of the movement of the vibratable member and thereby the frequency and the amount of the load change exerted on the specimen.

10. In a testing machine according to claim 6,

` Securing means 4 means for damping the amplitude oi said member; means ior imparting an initialor pre-load on said means in the nature of springs and thereby on the specimen; said means for. imparting a vibratory impulse being adjustable so as to vary the frequency oi said impulse; the damping means being adjustable so as to vary the damping eiect; coordination of the adjustments of the damping means and of the vibration means determining together with the natural frequency oi' the system the frequency and amplitude of the movement o! the vibratable member and thereby the frequency and the amount of the load change exerted on the specimen.

11.-In a device for testing materials, a substantially rigid base member, a pair of securing means for attaching,` two different points i a testingspeclmen, a vibratable member guided by said base member, means for imparting vibratory motion to said vlbratable member, a resilient element, one of said securing means being rigidly attached to one of said members. the other being attached to one side oi said resilient element. the opposite 'side of said l resilient element being attached to the other member, the arrangement being thereby such that said resilient member and a specimen connected to said securing means are arranged in series between said base member and said svibratable member, and means for `nre-loading said resilient element and a specimen connected tosaid securing means.

12. In a device for testing materials, a\substantially rigid base member, a pair oi securing means for attaching two diilerent points oi a testing specimen, a vibratabie member, means for imparting vibratory motion to said vibratable member, a nrst resilient element element, a second resilient element, said iirst resilient element being inserted between said base member and said vibratable member, the one oi said securing means being attached to one o! said members, the other securing means being attached to one side oi said second resilient element, the opposite side oi said second resilient element being attached to the other member, the arrangement being thereby such that a specimen connected to said two securing means, said vibratable member and said resilient members are arranged in series between two points of base member. and means for imparting an initial load to said resilient members and a specimen connected to said securing means.

13. In a device tor testing materials, a substantially rigid base member, a pair oi. securing means for attaching two diierent points of a testing specimen, a vibratable member guided by said base, means for imparting vibratory motion to said vibratable member, vibration-transmitting means adapted to yieldingly exert aA torce between two oi its points and having a natural frequency oi relative movement oi those points. one of said 'securing means being attached to one of said members, the other securing means being attached to the one aforesaid point of said vibration-transmittingmeans, the other aforesaid point oi said vibration-transmitting means being `attached to the other member, the arrangement being thereby such that a specimen connected to said securing means and the part of said vibration-transmitting means between its said two points are arranged in series between said base member and said vibratable member, and means for imposing a pre-loading on `said vibration-transmitting means and to a specimen to be tested.

RUPEN EKSERGIAN.

CERTIFICATE OF CORRECTION.

Reissue No. 22,1416. January l1, 19141;.

RUPEN EKSERGIAN.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction au follows: Page 1, first column, line 28, for "turned'l read -tuned; and that the said Letters Patent should be read with this correction therein that the same may confom to the record of the case in the Patent Office.

signed and sealed this 50m any of my, A. D. 1914A.

v Leslie Frazer (seal) Acting Cnmmissioner or Patents. 

